title: On the stereochemical inertness of the auride lone pair: ab initio studies of AAu (A = K, Rb, Cs).
abstract: The "lone" 6s electron pair often plays a key role in determining the structure and physical properties of compounds containing sixth-row elements in their lower oxidation states: Tl(+), Pb(2+), and Bi(3+) with the [Xe]4f(14)5d(10)6s(2) electronic configuration. The lone pairs on these ions are associated with reduced structural symmetries, including ferroelectric instabilities and other important phenomena. Here we consider the isoelectronic auride Au(-) ion with the [Xe]4f(14)5d(10)6s(2) electronic configuration. Ab initio density functional theory methods are employed to probe the effect of the 6s lone pair in alkali-metal aurides (KAu, RbAu, and CsAu) with the CsCl structure. The dielectric constants, Born effective charges, and structural instabilities suggest that the 6s lone pair on the Au(-) anion is stereochemically inert to minor mechanical and electrical perturbation. Pressures greater than 14 GPa, however, lead to reorganization of the electronic structure of CsAu and activate lone-pair involvement and Au-Au interactions in bonding, resulting in a transformation from the cubic CsCl structure type to an orthorhombic Cmcm structure featuring zigzag Au-Au chains.
authors.affiliation: Materials Research Laboratory, University of California, Santa Barbara, Santa Barbara, California 93106, USA.
authors.forename: Maosheng
authors.initials: M
authors.lastname: Miao
authors.forename: Jakoah
authors.initials: J
authors.lastname: Brgoch
authors.forename: Aditi
authors.initials: A
authors.lastname: Krishnapriyan
authors.forename: Abby
authors.initials: A
authors.lastname: Goldman
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Kurzman
authors.forename: Ram
authors.initials: R
authors.lastname: Seshadri